Detection system for protecting anodes in flowing mercury cathode electrolytic cells

ABSTRACT

Describes an apparatus for protecting adjustable anodes in a horizontal mercury cell by measuring the flow of current in the bus line to the anodes, measuring variations of voltage between an anode and a flowing mercury cathode and adjusting the space between the anodes and the cathodes in accordance with the output signal of the measurement of current to the anodes and voltage between the anodes and the cathodes.

United States Patent Adachi et al.

1 Dec. 16, 1975 DETECTION SYSTEM FOR PROTECTING ANODES IN FLOWINGMERCURY CATHODE ELECTROLYTIC CELLS Inventors: Yoichi Adachi; YoshiharuHarada,

both of Tokyo, Japan Assignee: Mitsui & Co. Ltd., Tokyo, Japan Filed:Sept. 8, 1972 Appl. No.: 287,490

Foreign Application Priority Data Sept. 13,1971 Japan 467l019 US. Cl.204/99; 204/220; 204/225; 204/228 Int. C13. C25B 1/40; C25B 15/04; C25B15/06 Field of Search 340/253, 248 E, 419; 204/225, 219, 220, 99, 228

References Cited UNITED STATES PATENTS Sabbah et a1 340/253 E UX2,459,186 l/l949 Sherman 340/253. R X 3,644,190 2/1972 Weist et a1 .1204/228 3,689,398 9/1972 Caleffi 204/228 X 3,723,285 3/1973 Daga et a1204/228 FOREIGN PATENTS OR APPLICATIONS 1,239,835 7/1971 United Kingdom204/228 1,167,001 10/1969 United Kingdom 204/99 1,212,488 11/1970 UnitedKingdom 204/225 Primary Exanzii1erG. L. Kaplan Attorney, Agent, orFirmHammond & Littell 5 7] ABSTRACT 7 Claims, 5 Drawing Figures U.S.Patent Dec. 16, 1975 Sheet10f3 3,926,750

U.S. Patent Dec. 16, 1975 Sheet 3 of3 3,926,750

DETECTION SYSTEM FOR PROTECTING ANODES IN FLOWING MERCURY CATHODEELECTROLYTIC CELLS This invention relates to detection systems forprotecting anodes in flowing mercury cathode horizontal electrolyticcell and more particularly to a detection system for protecting anodesin a flowing mercury cath ode electrolytic cell from damages due to ashort circuit between the flowing mercury cathode and the anodes whichcomprise such a material as graphite or titanium.

Horizontal mercury electrolytic cells are well known in the art. In atypical horizontal mercury electrolytic cell, mercury which forms thecathode of the cell is flowed over the bottom of the slightly inclinedcell from its one end to the other end in the form of a uniform layer,anodes are arranged above the flowing mercury cathode and spacedtherefrom at a short distance, for example, 1.5mm to 3.5mm, and brine isused as the electrolyte to electrolyse it into sodium and chlorine.

There is no problem when the mercury cathode is flowing with its smoothsurface, however, a part or parts of the mercury surface are oftenraised, for example, by foreign matters mixed therewith. In such a case,the space between the anodes and the raised parts of the flowing mercurycathode become narrow, thus the electric current concentrates at suchnarrow portions and if this condition persists, the anodes will bedamaged, consequently the cell will become inoperable.

When the cell is operated with an increased space between theelectrodes, it can be operated safely since the current distribution inthe cell will be improved and the potentiality in occurrence of theabove-mentioned tendency will be reduced, however, such an increasedspace between the electrodes will lead to an increase of the cellvoltage resulting in power loss.

Therefore, protection devices required for the opera tion ofelectrolytic cells are preferably capable of reducing the cell voltageas low as possible in a normal operating condition and capable ofeliminating any abnormality before anodes are damaged when such anabnormal condition takes place.

Conventional detection systems including so called a bus bar overcurrentdetection system which detects the current through bus bars betweenvarious electrolytic cells and when the detected current reaches a pointhigher than a set point, a protection device is operated, and a lowvoltage detection system which detects the cell voltage at variousportions of a cell and when the detected voltage reaches to a pointlower than a set point a protection device is operated, however, withsuch a conventional system for detecting only a single factor, a normaloperation condition is not completely distinguishable from an abnormaloperating condition, and vice versa. Thus cells should either be set soas to permit an abnormal operating condition to a certain extent orarranged so as to operate at a high safety level more than necessary.

So-called a voltage variation rate detecting system is also well knownin the art, which system detects a cell voltage and when thetime/variation rate (dv/dt) of the detected voltage reaches to a pointhigher than a set point, a protection device is actuated. This system isregarded as very reasonable, since in the course to the short-circuitingbetween the electrodes, the initial time/variation rate (dv/dt) of thecell voltage is extremely low but finally it shows a substantial value,

however, variations in voltage is also caused by other factors, forexample, changes of the mercury surface due to the surging of a mercurypump, or changes of the cathode surface due to variations in gaseouschlorine suction pressure. Such a system, therefore. has a disadvantagethat it can not protect anodes reliably since it lacks in ability ofdistinguishing variations in voltage due to the short-circuiting betweenthe electrodes from variations in voltage due to other factors than theshort-circuiting.

The object of the present invention, therefore, is to provide adetection system for protecting anodes in flowing mercury cathodeelectrolytic cells from damages, which system eliminates disadvantagesof conventional current detection systems and voltage detection systemsand which is capable of distinguishing the normal operation fromabnormal operations of cells by detecting it as a combination of voltageand current, such a function has never been fulfilled with conventionalsystems since the normal operation is not distinguishable from abnormaloperations by detecting it either as current or voltage alone.

According to the present invention, there is provided a detection systemfor protecting anodes in a flowing mercury cathode electrolytic cell inwhich a plurality of anodes are suspended over the flowing mercurycathode leaving a predetermined space therebetween, which systemcomprises detecting a bus current, detecting a cell voltage, andgenerating an output signal when a resultant value of said detected buscurrent and cell voltage exceeds a predetermined value so that a displaylamp or an anode elevator may be actuated by said signal.

A preferred embodiment of the invention has been chosen for purpose ofillustration and description and is shown in the accompanying drawingsforming a part of this specification, wherein:

FIG. 1 is a vertical sectional view of a typical flowing mercury cathodeelectrolytic cell to which the present invention may be applied;

FIG. 2 is a schematic diagram showing a part of the cathode isabnormally raised whereby the space be tween the cathode and an anode isnarrowed;

FIG. 3 are graphs respectively showing variations in bus current andcell voltage during the normal opera tion and at the occurrence of anabnormal relation between the anodes and the cathode in the cell;

FIG. 4 is a circuit diagram of an electrolytic cell in which the presentinvention is embodied; and

FIG. 5 is a preferred embodiment of the circuit arrangement of thesystem of the present invention.

Referring to FIG. 1, a typical flowing mercury cathode cell 1 comprisesa plurality of, for example, fourteen suspended anodes 2 arranged in tworows. The anodes 2 are fed with current from a power source (not shown)through a bus 3 and bus bars 4. Mercury is introduced into the cell 1through its inlet end and flows over the bottom wall 5 forming asubstantially flat layer 6 flowing toward an outlet end of the cell. Theanodes 2 are suspended in the cell leaving a predetermined space betweentheir lower surfaces and the surface of the flowing mercury cathodelayer 6 and the space therebetween may be manually or automatically regulated by an anode elevator (not shown).

FIG. 2 shows a condition in which the space between an anode 2 and thecathode 6 is narrowed due to an abnormally raised portion 7 of thecathode. Variations in bus current and cell voltage due to such anabnormal 3 condition are shown in FIG. 3.

The upper part of FIG. 3 is a graph showing the relationship between theanodes (the order thereof being plotted on the abscissa) and the buscurrent (on the ordinate),in which curve A shows a substantially uniformcurrent distribution when the space between all of the anodes and theflowing mercury cathode is normally maintained, while the lower part ofFIG. 3 is a graph showing a substantially uniform cell voltagedistribution curve B during the ideal operating condition of the cell.Curve C shows an increased current when the space between one of theanodes (for example, the fourth anode) and the flowing mercury cathodehas been narrowed, and curve D shows a corresponding local voltage dropin such an abnormal condition.

The system of the present invention provides a circuit which detects abus current of each anode in an electrolytic cell and a correspondingcell voltage between a particular anode and the flowing mercury cathode,and generates an output signal when a resultant value of the detectedbus current and cell voltage has reached a set value to indicate anabnormal condition taking place between the particular anode and thecathode so as to prevent the anode from being damaged.

A preferred embodiment of the circuit arrangement of the system of thepresent invention is shown in FIG. 4 in association with the anodes inthe cell 1. The circuit comprises a power circuit and a detector unit,which power circuit is provided with a common power source 10. Theoutput of the common power source is respectively connected in parallelto a stationary bias power source 11, a regulating bias power source 12and a general power source 13. Preferably the common power source 10 isprovided with an automatic voltage regulator to minimize errors due tovariations in individual power sources. The stationary bias power source11 serves to regulate and equalize characteristic differences betweenamplifiers 15 corresponding to the anodes in the cell, and is connectedrespectively to the inputs of the amplifiers 15 in the unit 14 by a lead16 through variable resistors 17 respectively. It is desirable to usemagnetic amplifiers as the amplifiers 15.

For the sake of simplification, the fourth anode in the cell and itsassociated circuit will be described in detail as the representativesand other anodes and their associated circuits.

The regulating bias power source 12 serves to simultaneously regulatevarious set points which differ depending upon the specification of thecell and the type of the anodes relative to the whole cell, and isconnected to the inputs of the amplifiers 15 in the unit 14 through alead 18.

The general power source 13 serves to actuate the detector unit 14 andis connected to the input side of the unit 14 through a conductor 20having a switch 19 provided therein. The current from a bus 3 of thecell is fed to the detector unit 14 through a conductor 21. Voltagesbetween the individual anodes and the flowing mercury cathode arerespectively fed to the amplifiers 15 respectively through conductors22. The voltage input conductors 22 are connected to a relay 24 throughconductors 23 respectively. The relay 24 serves to actuate the switch 19provided in the conductor 20 of the general power source 13 and when thefeed'to the cell is discontinued, the relay 24 actuates the switch 19 toits open position to interrupt the feed to the detector unit 14 toprevent any unintended or erroneous actuation of the unit 14 during thediscontinuanceof the cell.

Referring now to FIG. 5 which shows a diagram of a preferred embodimentof the circuit of the detector unit 14 particularly in association withthe fourth anode in the cell.

The current input from a bus 34 of the fourth anode passes through acurrent input winding 25 of the associated amplifier 15 in the directionas shown by an arrow. A voltage between the fourth anode and the cathodepermits a current to be passed through a voltage input winding 26 in thedirection shown by an arrow. The current fed from the regulating biaspower source 12 through the conductor 18 passes through a regulatingbias winding 27 in the direction shown by an arrow. The variableresistors 17 serve to regulate the characteristics of individualamplifiers 15 relative to the anodes so as to equalize the outputs ofthe amplifier unit 14 under a predetermined condition.

The detector unit 15 is fed with current from the general power source13 through the conductor 20 and the outputs of the amplifiers 15 in theunit 14 are respectively connected to cathode element of Zener diodes 33through feedback windings 31 and conductors 32. The anode element ofeach of said diode 33 is connected to the base of a transistor 34 ofwhich collector is in turn connected to a relay 35. When the relay 35 isenergized, a contact 37 or 39 in conductor 36 or 38 leading respectivelyto actuating circuits (not shown) for a display lamp or for an automaticanode elevator for the particular anode, is moved to its closedposition.

Turns of each winding of said amplifier are suitably selected so thatwhen the cell is normally operated, i.e. the space between the anodesand the flowing mercury cathode is in normal condition thus a combinedvalue of an input current from the bus to the particular amplifier andan cell voltage which depends upon the electrical characteristic of thecell is below a set point, the relay 35 is maintained in stationarystate by the output of the amplifier, and the Zener diode 33 is providedso that when the combined value of the bus current and the cell voltagereaches the set point, the relay 35 is rapidly actuated.

With the arrangement of the present invention as set forth hereinabove,when the space between an anode, for example, the fourth and the flowingmercury cathode is unvaried or normal, the output of the particularamplifier 15 is incapable of energizing the relay 35, since the buscurrent from the bus 3-4 to the amplifier 15 associated with the fourthanode and the cell voltage remain unvaried. When the space between thefourth anode and the flowing mercury cathode, however, is narrowed dueto any abnormality, the current from the bus 34 to the amplifier 15increases (see curve C in FIG. 3) and the cell voltage at thecorresponding cell region drops accordingly (see curve D in FIG. 3),whereby the output of the magnetic amplifier 15 is increased until itreaches a Zener voltage (a set value) of the Zener diode 33 and a signalis fed to the base of the transistor 34 to actuate the relay 35. Thusthe relay 35 then operates to close the contact 37 in the conductor 36leading to the circuit for actuating the associated display lamp whichindicates the abnormal condition occurred in the fourth anode region, orthe contact 39 in the conductor 38 leading to the circuit for actuatingthe associated automatic anode elevator whereby the space between thefourth anode and the flowing mercury cathode may be widened todiscontinue the short circuit formed therebetween.

As will be evident from the foregoing description, certain aspects ofthe invention are not limited to the particular details set forth inthis specification. it is contemplated that various modifications willoccur to those skilled in the art and it is therefore intended thatappended claims shall cover such modifications as do not depart from thetrue spirit and scope of the invention.

What is claimed is:

1. Method for protecting anodes in a horizontal mercury cell byadjusting the distance between a plurality of anodes and the flowingmercury cathode in the cell for electrolyzing a conductive solutionwherein each of said anodes are adjustably suspended in said solution,which method comprises detecting the flow of current in a bus line ofeach anode to provide a first output signal, detecting voltage betweeneach anode and the flowing mercury cathode to provide a second outputsignal, combining said first and second signals to generate a summationsignal, generating an output signal when said summation signal exceeds apredetermined value, and energizing means for adjusting the distancebetween said anode and the cathode.

2. In an electrolytic cell for electrolyzing a conducting solution, saidcell comprising a plurality of anodes having bus bars and a flowingmercury cathode, the improvement wherein control means are present forad justing the anodecathode spacing for each anode, said control meanscomprising means for detecting the flow of currentin a bus line of eachanode to provide a first output signal, means for detecting a voltagebetween each anode and the flowing mercury cathode to provide a secondoutput signal, means for combining said first and second signals togenerate a summation signal, means for generating a reference signal,means for comparing said summation signal and said reference signal,means for generating an output signal signal when the difference betweensaid summation signal and said reference signal exceeds a predeterminedamount, and means energized by said output signal for either signalingor adjusting the anode-cathode spacing.

3. The apparatus of claim 2, in which the means energized comprises arelay which controls a circuit to an automatic anode elevator.

4. The apparatus of claim 3, in which the means energized comprisesmagnetic amplifiers and Zener diodes adapted to transmit the summationsignal to said relay.

5. The apparatus of claim 2, wherein the means for signaling is adisplay lamp.

6. The apparatus of claim 2, wherein the means energized is an automaticanode elevator.

7. The apparatus of claim 2, in which the means energized comprises arelay which controls a circuit to a display lamp.

1. METHOD FOR PROTECTING ANODES IN A HORIZONTAL MERCURY CELL BYADJUSTING THE DISTANCE BETWEEN A PLUTALITY OF ANODES AND THE FLOWINGMERCURY CATHODE IN THE CELL FOR ELECTROLYZING A CONDUCTIVE SOLUTIONWHEREIN EACH OF SAID ANODES ARE ADJUSTABLY SUSPENDED IN SAID SOLUTION,WHICH METHOD COMPRISES DETECTING THE FLOW OF CURRENT IN A BUS LINE OFEACH ANODE TO PROVIDE A FIRST OUTPUT SIGNAL, DETECTING VOLTAGE BETWEENEACH ANODE AND THE FLOWING MERCURY CATHODE TO PROVIDE A SECOND OUTPUTSIGNAL, COMBINING SAID FIRST AND SECOND SIGNALS TO GENERATE A SUMMATIONSIGNAL, GENERATING AN OUTPUT SIGNAL WHEN SAID SUMMATION SIGNAL EXCEEDS APREDETRMINED VALUE, AND ENERGIZING MEANS FOR ADJUSTING THE DISTANCEBETWEEN SAID ANODE AND THE CATHODE.
 2. IN AN ELECTROLYTIC CELL FORELECTROLYZING A CONDUCTING SOLUTION, SAID CELL COMPRISING A PLURALITY OFANODES HAVING BUS BARS AND A FLOWING MERCURY CATHODE, THE IMPROVEMENTWHEREIN CONTROL MEANS ARE PRESENT FOR ADJUSTING THE ANODECAATHODESPACING FOR EACH ANODE, SAID CONTROL MEANS COMPRISING MEANS FORDETECTING THE FLOW OF CURRENT IN A BUS LINE OF EACH ANODE TO PROVIDE AFIRST OUTPUT SIGNAL, MEANS FOR DETECTING A VOLTAGE BETWEEN EACH ANODEAND THE FLOWING MERCURY CATHODE TO PROVIDE A SECOND OUTPUT SIGNAL, MEANSFOR COMBINING SAID FIRST AND SECOND SIGNALS TO GENERATE A SUMMATIONSIGNAL, MEANS FOR GENERATING A REFERENCE SIGNAL, MEANS FOR COMPRISINGSAID SUMMATION SIGNAL AND SAID REFERENCE SIGNAL, MEANS FOR GENERATING ANOUTPUT SIGNAL WHEN THE DIFFERENCE BETWEEN SAID SUMMATION SIGNAL AND SAIDREFERENCE SIGNAL EXCEEDS A PREDETERMINED AMOUNT, AND MEANS ENERGIZED BYSAID OUTPUT SIGNAL FOR EITHER SIGNALING OR ADJUSTING THE ANODECATHODESPACING.
 3. The apparatus of claim 2, in which the means energizedcomprises a relay which controls a circuit to an automatic anodeelevator.
 4. The apparatus of claim 3, in which the means energizedcomprises magnetic amplifiers and Zener diodes adapted to transmit thesummation signal to said relay.
 5. The apparatus of claim 2, wherein themeans for signaling is a display lamp.
 6. The apparatus of claim 2,wherein the means energized is an automatic anode elevator.
 7. Theapparatus of claim 2, in which the means energized comprises a relaywhich controls a circuit to a display lamp.